The need for effective means of combating airborne odors in homes and public building by odor masking or destruction is well established as is the dispensing of insect control materials, aromatherapy, antiseptics and disinfectants. Various kinds of vapor-dispensing devices have been employed for these purposes. Common types of dispensing devices are aerosol containers which propel minute droplets of a liquid composition into the air, dish-like devices that support a gelatinous material which releases vapor upon drying, and wicking devices in which the liquid to be vaporized is transported through a wick and exposed to air. Air freshening devices in which there is a slow release of vapor into the air from a liquid are well known in the art. See, e.g., U.S. Pat. No. 1,994,932; U.S. Pat. No. 2,597,195; U.S. Pat. No. 2,802,695; U.S. Pat. No. 2,804,291; U.S. Pat. No. 2,942,090; U.S. Pat. No. 3,550,853; U.S. Pat. No. 3,780,260; U.S. Pat. No. 4,084,079; U.S. Pat. No. 4,286,754; U.S. Pat. No. 4,413,779; U.S. Pat. No. 4,454,987; U.S. Pat. No. 4,913,350; and U.S. Pat. No. 5,000,383. Also well known are wicking devices in which vaporization is enhanced by a heating source. See, e.g., U.S. Pat. No. 3,288,556; U.S. Pat. No. 3,431,393; U.S. Pat. No. 3,482,929; U.S. Pat. No. 3,633,881; U.S. Pat. No. 4,020,321; U.S. Pat. No. 4,968,487; U.S. Pat. No. 5,038,394; U.S. Pat. No. 5,290,546; U.S. Pat. No. 5,364,027; and U.S. Pat. No. 6,478,440. See also, U.S. Pat. No. 4,549,250; U.S. Pat. No. 4,837,421; U.S. Pat. No. 4,849,606; U.S. Pat. No. 5,556,192; U.S. Pat. No. 5,937,140; and WO02/30220.
However, current devices that rely on evaporation of the liquid from a wick have the disadvantages of depleting the liquid in a reservoir at an uneven rate and composition. See, e.g., U.S. Pat. No. 4,663,081. The cause for the change in the rate of evaporation is frequently the result of the evaporative surface of the wick becoming partially clogged during the evaporation process with less volatile resins. Compositional changes in the released vapor over time are also the result of uneven evaporation due to the more volatile components of the liquid mixture evaporating faster and thereby leaving a disproportionately different composition in the liquid from the original composition.
Therefore, it is highly desirable to derive a mass transfer device that disperses liquid into a vapor while substantially maintaining the liquid composition at the original composition over the useful life of the device, for example, 30 days. Further, it is desirable to have the ability to control the rate at which the liquid is dispersed and control it by electrical or mechanical means using timers, sensors, switches, or remote devices. It is especially desirable to be able to start and stop the dispersion of liquid to the vapor phase at will or even disperse different liquid solutions at different times. Further still, active ingredients in some instances need to be stable in solution and released only upon reaction with a second liquid or a catalytic surface.